This invention relates to a quick coupling for plastic pipe and more particularly to arrangements accommodating the use of mechanical couplers for plastic pipes.
The coupling and uncoupling of sections of plastic pipe, particularly such as PVC (polyvinylchloride) or ABS (Polyacrylonitrile-Butadiene-Styrene) pipe, in a simple and effective manner as is done with metal pipe is desired. Plastic pipe, however, does not have the strength or rigidity of metal pipe and grooving it weakens it still more. Thus, for full effectiveness, special provisions must be made for joining sections of such pipe to prevent the pipe from separating at the joint.
In the prior art, various methods have been tried to link or couple plastic pipe together or with metal pipe and the methods used were those that related mostly to metal pipe and were frequently unsatisfactory. One such method is discussed in U.S. Pat. No. 3,695,638 issued to James Blakely. In the Blakely patent, which discloses a coupling for plastic pipe which is now marketed under the name Victaulic (a U.S. registered trademark) provided grooves near the end of the plastic pipe similar to that used in metallic pipe. Blakely's coupling utilizes a foot or key that meets the groove wall in a plastic pipe. Blakely discusses the problem in a key and groove coupling where the plastic pipe is in a deflected position and internal pressure increases, in which a shearing of the groove shoulder can occur resulting in the coupling parting. The coupling in Blakely has lateral wings on either side of the key to assist in reducing possible deflection of the plastic pipe.
U.S. Pat. No. 4,310,184 issued to Steve Campbell, discloses a connector sleeve for polyolefin pipe ends which takes advantage of the deformability of the polyolefin pipe. Campbell discloses the use of a metallic sleeve which has interior circumferential ribs which engage in mating relationship, exterior grooves that are formed in the exterior of the pipe ends to be joined. With such pipe ends butted together and the connector sleeve overlaying the joint, a conventional clamp having again interior circumferential ribs or ridges, engages the indentation on the sleeve where the interior circumferential ribs are formed.
In U.S. Pat. No. 2,967,067 issued to Heinrich Singer describes a connecting means for soft tubes and provides a connector fitting which uses tooth shaped protrusions that grip the plastic pipe.
U.S. Pat. No. 4,114,930 issued to Donald Perkins, et al describes a method for coupling plastic pipe in which the ends of the pipe are swedged over a tubular insert having exterior serrations and the tubing becomes permanently held between the insert and the sleeve. Such an arrangement is not feasible for rigid plastic pipe and has additional deficiency of interrupting the flow pattern of fluid through the pipe.
A different approach is used in U.S. Pat. No. 4,039,210 issued to Roy Wood, et al. A circumferential recess is formed on the outside surface of the pipe and this recessed area is further treated to form three circumferential grooves on the outside surface of the pipe. A first metal sleeve is inserted in the recess extending away from the groove furthest removed from the coupling end of the pipe. A split locking ring is inserted in the groove furthest removed from the coupling end of the pipe and a resilient gasket ring is inserted in the middle groove. A second metal sleeve is inserted in the recess abutting the lock ring and encasing the gasket ring in the middle groove. A second metal sleeve is indented so that it fits into the third groove, the groove nearest the coupling end of the pipe, retaining the grooved configuration. A third metal sleeve is slidably positioned encasing the lock ring and overlapping the first and second metal rings and this third metal sleeve is then fixed into position. It can readily be seen that the order in which the elements of the invention are put into position is important. The resilient gasket must be in position before the second metal sleeve is positioned and both the first and second metal sleeves and the lock ring must be positioned before the third metal sleeve can be put into place.
This complex arrangement then utilizes a metal clamp, such as the Victaulic clamp previously discussed to retain the pipes coupled together.